Currently it seems to be impossible to bootstrap go1.11.2 on the Raspberry Pi by using the go1.4 bootstrapper. Therefore I created a readily compiled go1.11.2 bootstrapper that is able to compile go1.11.2 for your Raspberry Pi. This repository already includes all the instructions you need to make it work.
Right now the current Go version within the Raspbian Stretch repositories is 1.7 (golang-go) or 1.8.1 (golang-1.8) which doesn’t meet expectations of many useful projects written in Go, that I have seen and use.